Welded blank assembly and method

ABSTRACT

A welded blank assembly is formed by welding first and second sheet metal pieces together at a weld joint. At least one of the sheet metal pieces includes a boron steel or press hardenable steel base material layer and an aluminum-based coating material layer, along with a weld notch where at least a portion of the coating material layer is removed before welding. An additional material can be provided during welding to influence weld joint composition and/or a secondary heat source can be used to heat and flow a protective material in a weld region of the blank assembly. The weld notch has a width that may be related to the width of a heat-affected zone formed during welding.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/930,916, filed on Jun. 28, 2013, which claims the benefit of U.S.Provisional Ser. Nos. 61/666,388 filed on Jun. 29, 2012; 61/701,909filed on Sep. 17, 2012; 61/731,497 filed on Nov. 30, 2012; and61/784,184 filed on Mar. 14, 2013. The entire contents of each of theaforementioned applications are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure generally relates to welded blank assemblies and,more particularly, to welding coated sheet metal pieces together to formwelded blank assemblies.

BACKGROUND

In an effort to improve resistance to corrosion, scaling and/or otherprocesses, sheet metal made of high-strength or hardenable steel alloysare now being made with one or more thin coating material layers, suchas aluminum- and zinc-based layers. Although these coating materiallayers can impart desirable qualities to the sheet metal, their presencecan contaminate welds, thereby reducing weld strength, integrity, etc.This is particularly true if the coated sheet metal piece is being buttwelded or lap welded to another sheet metal piece.

SUMMARY

In accordance with one embodiment, a method of making a welded blankassembly comprises the steps of: (a) providing first and second sheetmetal pieces, at least one of the first and second sheet metal piecescomprises: a base material layer of boron steel or press hardenablesteel having a thickness in a range from 0.5 mm to 2.0 mm, analuminum-based coating material layer having a thickness in a range from5 μm to 100 μm, and a weld notch located along an edge region of thesheet metal piece where at least a portion of the coating material layerhas been removed; (b) arranging the first and second sheet metal piecestogether at the edge region; (c) forming a weld pool between the firstand second sheet metal pieces at the edge region, wherein the weld poolcomprises constituents of the edge region; and (d) providing additionalmaterial to the weld pool to influence a composition of a weld jointthat is formed when the weld pool solidifies, the additional materialbeing provided with a composition and in an amount that, when the weldedblank assembly is subsequently heated and quenched in a heat treatingprocess, provides the heat treated weld joint with a hardness and/or atensile strength that is greater than that of at least one of the firstand second sheet metal pieces at a location away from the heat treatedweld joint.

In accordance with another embodiment, a method of making a welded blankassembly comprises the steps of: (a) providing first and second sheetmetal pieces, at least one of the first and second sheet metal piecescomprises: a base material layer of boron steel or press hardenablesteel having a thickness in a range from 0.5 mm to 2.0 mm, analuminum-based coating material layer having a thickness in a range from5 μm to 100 μm, and a weld notch located along an edge region of thesheet metal piece where at least a portion of the coating material layerhas been removed; (b) arranging the first and second sheet metal piecestogether at the edge region; (c) forming a weld pool between the firstand second sheet metal pieces at the edge region, wherein the weld poolcomprises constituents of the edge region; (d) solidifying the weld poolto form a weld joint that joins the first and second sheet metal piecestogether at a weld region of the welded blank assembly; and (e) using asecondary heat source to heat a protective material comprising aluminumso that the protective material flows in the weld region after the weldpool is at least partially solidified.

In accordance with yet another embodiment, a method of making a weldedblank assembly comprises the steps of: (a) providing first and secondsheet metal pieces, at least one of the first and second sheet metalpieces comprises: a base material layer of boron steel or presshardenable steel having a thickness in a range from 0.5 mm to 2.0 mm, analuminum-based coating material layer having a thickness in a range from5 μm to 100 μm, and a weld notch located along an edge region of thesheet metal piece where at least a portion of the coating material layerhas been removed; (b) arranging the first and second sheet metal piecestogether at the edge region; (c) forming a weld pool between the firstand second sheet metal pieces at the edge region, wherein the weld poolcomprises constituents of the edge region; and (d) solidifying the weldpool to form a weld joint that joins the first and second sheet metalpieces together at a weld region of the welded blank assembly with aheat affected zone adjacent the formed weld joint, wherein each weldnotch is provided with a width so that a combined weld notch width is ina range from 1.5 to 4.0 times a width of the heat-affected zone.

DRAWINGS

Preferred exemplary embodiments will hereinafter be described inconjunction with the appended drawings, wherein like designations denotelike elements, and wherein:

FIGS. 1A-C are cross-sectional views of a conventional weld jointjoining sheet metal pieces that did not have weld notches formed thereinbefore welding;

FIG. 2 is a perspective view of an edge region of an exemplary sheetmetal piece, including weld notches on opposite sides of the sheet metalpiece formed by laser ablation;

FIG. 3 is a cross-sectional view of a portion of the sheet metal pieceof FIG. 2;

FIG. 4 is a perspective view of an exemplary welding process beingperformed on aligned sheet metal pieces with weld notches in order toform a welded blank assembly;

FIG. 5 is a perspective view of another exemplary welding process beingperformed on aligned sheet metal pieces with weld notches, whereadditional material is added to the weld joint in the form of a wire;

FIG. 6 is a perspective view of another exemplary welding process beingperformed on aligned sheet metal pieces with weld notches, whereadditional material is added to the weld joint in the form of a powder;

FIG. 7 is a cross-sectional view of the welded blank assembly of FIG. 4taken before laser welding;

FIG. 8 is a cross-sectional view of the welded blank assembly of FIG. 4taken after laser welding;

FIG. 9 is a cross-sectional view of an embodiment of the welded blankassembly, where the welded sheet metal pieces have the same thickness;and

FIG. 10 is a cross-sectional view of an embodiment of the welded blankassembly, where only one of the welded sheet metal pieces has weldnotches.

DETAILED DESCRIPTION

The welded blank assemblies disclosed herein can be made from sheetmetal pieces having weld notches located along one or more edges to bewelded, where the weld notches are characterized by the absence ofcertain material constituents so that they do not unacceptablycontaminate nearby welds. For instance, a welded blank assembly can beproduced from sheet metal pieces with material from one or more coatingmaterial layers reduced or removed at a weld notch located along thesheet metal edge. This, in turn, can prevent contamination by thecoating material layers of a nearby weld joint formed along the sheetmetal edge when making the welded blank assembly and thereby preservethe strength and/or durability of the weld joint in subsequent processesor during its service life.

Turning first to FIGS. 1A-C, there are shown some of the steps involvedwith manufacturing a conventional tailor-welded blank 10 that includesthick and thin sheet metal pieces 12, 12′ laser welded together in anedge-to-edge fashion. According to this example, each of the sheet metalpieces 12, 12′ has a base material layer 14 and multiple thin materiallayers 16, 18 covering opposite surfaces of the base material layer. Asis appreciated by those skilled in the art, there are numerous materiallayers that could be found on sheet metal stock, including various typesof surface treatments, coating material layers such as aluminum- andzinc-based material layers (e.g., aluminum compounds), oils and otheroxidation preventing substances, contaminants from the manufacturing ormaterial handling processes, and oxidation layers, to name but a few.Once the two sheet metal pieces are brought together in abutment, alaser beam or other welding tool is used to melt some of the sheet metallocated in edge regions 20, 20′ so that a certain amount of the thinmaterial layers 16, 18 becomes embedded within the resulting weld joint22. Unless first removed, these unwanted constituents could have anegative impact on the overall strength and quality of the weld joint.

Referring to FIG. 2, there is shown an exemplary sheet metal piece 112that may be used to form a welded blank assembly while avoiding unwantedconstituents in the resulting weld joint. The sheet metal piece 112 isshown during a laser ablation process and may be subsequently welded toan adjacent piece along an edge region 120. The sheet metal piece 112includes opposite first and second sides 124, 126, and the edge region120 includes an edge 128 that is to be welded. The particular edgeregion 120 shown in FIG. 2 includes two weld notches 130, where the twoweld notches extend along the edge region on opposite sides 124, 126 ofthe sheet metal piece. The weld notch 130 on the visible side 124 isshown as it is being formed. Each weld notch 130 is defined by a firstnotch surface 132 and a second notch surface 134 that intersect or joineach other. Though shown with generally perpendicular first and secondnotch surfaces 132, 134 along a single, straight edge region 120, theweld notches may be configured in numerous ways. For example, a weldnotch can: include one or more off-axis or offset notch surfaces, have auniform or non-uniform depth and/or width, differ from other weldnotches located on the same sheet metal piece in terms of size, shape,configuration, etc., or be part of an edge region located along astraight edge, multiple straight edges, a curved edge, multiple curvededges, or some other part of the sheet metal piece, to cite severalpossibilities.

In the illustrated laser ablation process, a laser beam 102 is directedat the edge region 120 from a laser source (not shown) in order to formthe weld notch 130. Energy provided by the laser beam 102 is transferredto the sheet metal piece 112 in the form of thermal energy at anablasion site or laser spot 104, melting and/or vaporizing material atthe ablation site in order to remove material from one or more layers ofthe sheet metal piece. The laser beam 102 follows a path 106 along theedge region 120 to form the weld notch 130 in the desired configuration.For sheet metal pieces that include base, intermediate, and coatingmaterial layers as described below, the weld notch 130 may be formed byremoving all or some of the coating material layer, all or some of theintermediate material layer, and/or some of the base material layeralong the edge region 120. The sheet metal piece 112 may be heldstationary while the laser beam 102 moves along the path 106 (in thex-axis direction in FIG. 2). Alternatively, the sheet metal piece 112can be moved or indexed while the laser beam 102 remains stationary, orboth the laser beam 102 and the sheet metal piece 112 can be moved sothat the laser beam follows the desired path. Some portions of the path106 can be straight or rectilinear, as shown in FIG. 2, while otherportions can be contoured, curved or curvilinear; it is not necessaryfor the weld notch 130 to follow a straight path 106, as paths havingother configurations can be followed instead. Any of the above-mentionedembodiments may be carried out while the sheet metal piece is in ahorizontal, vertical or angled orientation.

Any suitable laser or other comparable light emitting device may be usedto form the weld notches, and may do so using a variety of operating orequipment parameters. In one example, the laser source is a Q-switchedlaser, but other continuous wave and pulsed laser types may be usedinstead, such as various nanosecond, femtosecond and picosecond pulsedlasers. The illustrated laser spot 104 is rectangular, but the laserspot or footprint 104 can be any shape, such as round, square,elliptical, or any other suitable shape. Non-limiting examples ofselectable or adjustable operating parameters for the laser source mayinclude: laser power, pulse frequency, pulse width, pulse energy, pulsepower, duty cycle, spot area, the overlap between successive laserpulses, and the speed of laser source relative to the sheet metal piece112, to cite a few possibilities. Any combination of these operatingparameters may be selected and controlled based on the particular needsof the application.

The laser ablation process can be performed in any number of differentways depending on the desired number, location and/or shape of the weldnotches or other factors. For example, a second laser beam may beemployed to overlap the laser beam 102 or to simultaneously removematerial from a different portion of the sheet metal piece, such as theopposite side 126 or the actual edge surface 128; the laser beam mayform a non-zero angle of incidence with the sheet metal piece; the sheetmetal piece may be oriented at an inclined angle to help control theflow of molten expulsed material; the laser beam may be directed at anupward- or downward-facing side of the sheet metal piece; or the processmay be performed on sheet metal that is continuously fed through theprocess from a roll, to cite several possibilities. In addition,processes other than laser ablation may be used to form the weld notch130, such as a mechanical ablasion process that uses a scraper tool, awire brush, or other tool to selectively remove material from the edgeregion 120.

FIG. 3 is a cross-section showing the edge region 120 of the sheet metalpiece 112 from FIG. 2. The illustrated sheet metal piece 112 includesmultiple material layers, including the base material layer 114,intermediate material layers 116, and coating material layers 118. Inthis embodiment, the base material layer 114 is the central or corematerial layer (e.g., a steel core) and is sandwiched between theintermediate material layers 116 and the coating material layers 118.The base material layer 114 makes up the majority of the thickness T ofthe sheet metal piece 112 and thus may contribute significantly to themechanical properties of the sheet metal piece. The coating materiallayers 118 are located over opposite surfaces of the base material layer114 and are the outermost layers of the sheet metal piece 112. Eachcoating material layer 118 is relatively thin with respect to the basematerial layer 114 and may be selected to enhance one or morecharacteristics of the sheet metal piece (e.g., corrosion resistance,hardness, weight, formability, appearance, etc.). The coating materiallayer 118 may also be selected for use or compatibility with subsequentprocesses, such as heat treatment or interdiffusion processes, forexample.

Each intermediate material layer 116 is located between the base layer114 and one of the coating material layers 118, and is in contact witheach in this embodiment. In one embodiment, the intermediate materiallayer 116 includes at least one constituent in common with each of theimmediately adjacent layers 114, 118, such as an atomic element orchemical compound. The intermediate material layer 116 may be a reactionproduct of the base and coating material layers 114, 118. For example, adip coating process, in which the base material layer is immersed orpasses through a molten bath of the coating layer material, can resultin a chemical reaction at the interface of the base material layer andthe molten bath, and the reaction product is the intermediate materiallayer 116. In one specific example of such a dip coating process, thebase material layer 114 is made of a high-strength or hardenable steelalloy and the coating material layer 118 is an aluminum alloy. Themolten bath of aluminum alloy reacts with the base material layer at itssurface to form the intermediate material layer 116, which includesiron-aluminum (Fe_(x)Al_(y)) intermetallic compounds such as Fe₂Al₅. Theintermediate material layer 116 can have a higher content of the basematerial layer constituent (e.g., iron) closer to the base materiallayer 114, and a higher content of the coating material layerconstituent (e.g., aluminum) closer to the coating material layer 118.Though shown in FIG. 3 as a perfectly planar layer with a constantthickness, the intermediate material layer 116 may be more irregularalong its opposite surfaces than is illustrated here. The sheet metalpiece 112 may include other, additional material layers as well, and isnot limited to the particular arrangement described here.

One specific example of a multi-layered sheet metal piece, such as thatshown in FIG. 3, useful for forming body and structural components inthe automotive and other industries is a coated steel product in whichthe base material layer 114 is made from steel in any of its variouspossible compositions. In one particular embodiment, the base materiallayer 114 is a high-strength or hardenable steel alloy such as a boronsteel alloy, dual phase steel, press hardened steel (PHS) or ahigh-strength low-alloy (HSLA) steel. Such materials, while strong fortheir weight, often require heat treating processes to attain thehigh-strength properties and/or can only be formed at high temperatures.The coating material layer 118 may be selected to help prevent oxidationduring heat treatment, to be lighter in weight than the base materiallayer 114, and/or to interdiffuse with the other layers of the sheetmetal piece 112 during subsequent heat treatment. In one embodiment, thecoating material layer 118 is an aluminum alloy, such as an Al-silicone(Al—Si) alloy. Other possible compositions for coating material layer118 include pure aluminum or zinc and its alloys or compounds (e.g.,where the underlying material is galvanized). Where the base materiallayer 114 is steel and the coating material layer 118 comprisesaluminum, the intermediate material layer 116 may include iron andaluminum in the form of intermetallic compounds such as FeAl, FeAl₂,Fe₃Al or Fe₂Al₅ or various combinations thereof. The intermediatematerial layer 116 may also include an alloy of constituents fromadjacent layers.

Exemplary material layer thicknesses range from about 0.5 mm to about2.0 mm for the base material layer 114, from about 1 μm to about 15 μmfor the intermediate layer 116, and from about 5 μm to about 100 μm forthe coating material layer 118. In another example, material layerthicknesses range from about 0.5 mm to about 1.0 mm for the basematerial layer 114, from about 5 μm to about 10 μm for the intermediatelayer 116, and from about 15 μm to about 50 μm for the coating materiallayer 118. In one embodiment, the combined thickness of the intermediateand coating material layers 116, 118 is in a range from about 15 μm toabout 25 μm, and the intermediate material layer is about 20-30% of thecombined thickness. For instance, the combined thickness of layers 116,118 may be about 20 μm, where the intermediate material layer is about4-6 μm thick, and the coating material layer makes up the remainder ofthe combined thickness. Of course, these ranges are non-limiting, asindividual layer thicknesses depend on several factors specific to theapplication and/or the types of materials employed. For example, thebase material layer 114 can be a material other than steel, such asalloys of aluminum, magnesium, titanium, or some other suitablematerials. The method described herein may be used with sheet metalpieces having more or less material layers than shown in the figures.Skilled artisans will also appreciate that the figures are notnecessarily to scale and that the relative thicknesses of layers 114-118may differ from those illustrated in the drawings.

Referring again to FIG. 3, the weld notch 130 on the first side 124 ofthe sheet metal piece will be described. This description applies to theweld notch 130 on the opposite second side 126 as well, in this example.The weld notch 130 is a portion of the edge region 120 of the sheetmetal piece 112 where some material has been removed or omitted from theotherwise uniform layered structure. The weld notch 130 promotes a highquality weld joint along edge 128 when the sheet metal piece is weldedto another piece, and may do so via a configuration that reduces oreliminates the amount of the coating material layer 118 and/or theintermediate material layer 116 that becomes part of a subsequent weldjoint. The weld notch is particularly useful where the coating materiallayer 118 includes one or more constituents that form discontinuities inor would otherwise weaken the resulting weld joint if included therein.The weld notch 130 has a characteristic notch width W and notch depth D,each being relatively constant along the length of edge 128 in thisparticular embodiment. The notch width W is the distance from edge 128to the first notch surface 132, and the notch depth D is the distancefrom the outer surface of the coating material layer 118 to the secondnotch surface 134. Where the weld notch 130 is square with the sheetmetal piece, as shown in this particular example, the notch width W isequal to the width of the second notch surface 134, and the notch depthD is equal to the width of the first notch surface 132.

The dimensions of the weld notch 130 may be related to the thickness Tof the sheet metal piece, to the intended size of the weld joint to beformed at edge 128, and/or to one or more material layer thicknesses. Inone embodiment, the notch width W is in a range from about 0.5 to about1.5 times the thickness T. In another embodiment, the notch width W isin a range from about 0.5 mm to about 4 mm. The notch width W may alsobe at least one half of the width of the intended weld joint. The notchdepth D for the example shown in FIG. 3 is greater than the thickness ofthe coating material layer 118 and less than the combined thickness ofthe intermediate and coating material layers 116, 118. But this differsin some of the other exemplary embodiments.

The weld notch 130 can also be described with relation to certaincharacteristics of the notch surfaces 132, 134. For example, in theembodiment of FIG. 3, the first notch surface 132 includes material fromboth the intermediate material layer 116 and the coating material layer118. The second notch surface 134 includes material from theintermediate material layer 116 only, and the first and second notchsurfaces intersect along an edge 136 that is positioned or located inthe intermediate material layer. Thus, in this particular example, theweld notch 130 is formed in the sheet metal piece 112 by removing theentire coating material layer 118 and a portion of the intermediatematerial layer 116 along edge region 120. In other examples, the weldnotch may be formed by removing only a portion of the coating materiallayer 118, or by removing the entire coating and intermediate materiallayers 118, 116 and a portion of the base material layer 114. Each ofthe notch surfaces 132, 134 may also include striations, witness lines,or other indicators of the type of process used to remove material atthe weld notch location. Ablation processes such as laser ablation ormechanical ablation can form notch surfaces with different surfacecharacteristics, and the welded blank assemblies described herein mayuse sheet metal pieces with a variety of different weld notches.

Referring now to FIG. 4, there is shown an exemplary welding process forforming a welded blank assembly 140 from two coated sheet metal pieces112, 112′. For simplicity in the following description, the primedesignation in the numerals will sometimes be omitted when referringgenerally to certain features that both sheet metal pieces include, andit will be used when referring to features of a specific one of thesheet metal pieces. In the illustrated process, the edge regions 120 ofthe two sheet metal pieces 112 are aligned with respective edges 128contacting one another. A high-powered laser beam 142 is directed towardthe aligned edge regions 120 and impinges the sheet metal pieces 112 ata laser spot 144. The laser beam 142 delivers energy to the laser spot144 that is sufficient to locally melt material from each of the sheetmetal pieces 112, thereby forming a weld pool 146 that includes moltenmaterial from both sheet metal pieces. As the laser beam 142 movesforward or advances along the aligned edge regions 120 (in the positivex-direction in FIG. 4), the portion of the weld pool 146 behind thelaser beam (in the negative x-direction) solidifies to form a weld joint148. The resulting weld joint 148 joins the two sheet metal pieces 112and is located in a weld region 150 of the welded blank assembly 140.

The weld joint 148 may be substantially free of material from at leastone of the coating material layer(s) 116, 118. This is due at least inpart to the weld notches 130 being provided along the edge regions 120,where material from the coating layer(s) has been removed. In thisparticular example, each of the illustrated sheet metal pieces 112 has adifferent thickness (i.e., a tailor welded blank) and is prepared, as inFIGS. 2 and 3, with weld notches 130 formed along opposite sides 124,126 of the respective edge region 120. This and other examples of weldedblank assemblies are subsequently described in greater detail. It isalso noted that, although the illustrated blank assembly 140 includes asingle weld joint 148, the welded blank assembly may be formed from morethan two sheet metal pieces 112 with more than one weld joint 148. Theblank assembly 140 may alternatively or additionally include one or morecurvilinear weld joints, in which at least a portion of the weld jointis curve-shaped and formed along curved or contoured edges 128 and/oredge regions 120.

Other process steps may be performed to improve the quality of theresulting weld joint 148, such as by providing additional material tothe weld pool 146 in order to control the composition, size and/or shapeof the resulting weld joint 148. FIG. 5 shows one example, where theadditional material is in the form of a metal wire 158 that is fedtoward the laser spot 144 as the laser beam moves along the aligned edgeregions 120. The material from the metal wire 158 melts along withmaterial from the sheet metal pieces 112 so that the weld pool 146 andthe resulting weld joint 148 include the additional material. This canhave the effect of diluting the weld pool 146 with respect to certainunwanted constituents (i.e., residual constituents that were notcompletely removed from the coating and intermediate layers 118, 116).For example, it is sometimes the case that residual coating material ispresent at the aligned edge regions 120 even after an ablation processforms the weld notches 130. This may be due to splatter from the laserablation process or coating material that has been smeared or wipedalong edges 128 during previous shearing operations. Unwantedconstituents may also include oxides or other corrosion products presentalong the edge regions. Diluting the weld pool 146 with desirableadditional material can help drive out any residual unwantedconstituents, which may be less soluble in the weld pool.

The welding process may also include the addition of a protectivecoating 154 or other additional material over the resulting weld joint148, as shown in FIG. 6. The protective coating 154 may be applied toprotect the weld region 150 from oxidation while the blank assembly 140awaits metal-forming or other subsequent processes. The protectivecoating 154 can be a corrosion-resistant material, such as acorrosion-resistant metal or an organic material (e.g., oil, wax, orpolymer-based). The coating 154 may be applied in solid or liquid form,depending on the composition. In the example of FIG. 6, the materialthat forms the coating 154 is applied as a powder material 156 justbehind the laser spot 144, where residual heat from the laser processmelts the powder material so that it flows and coats the weld joint 148and/or other portions of the weld region 150. A secondary heatingprocess, such as an additional laser beam or other heat source, may beemployed to help the coating material flow in the weld region. Theprotective coating may have one or more constituents in common with thecoating material layer 118 of the sheet metal piece(s). In oneembodiment, the protective coating 154 is aluminum or an Al-alloy andmay be formulated to replace material previously removed from theindividual sheet metal pieces 112 when the weld notches 130 were formed.In the case where the sheet metal pieces 112 are Al-coated steel, theprotective coating 154 is thus available to interdiffuse with the steelin the weld region in subsequent heat treating and/or hot-formingprocesses. Where organic materials are used to form the protectivecoating 154, the coating can be burned off in such subsequent processes,or otherwise later removed.

The additional material, whether provided in wire form, powder form orotherwise, is preferably selected to be compatible with the materialsalready included in the weld pool. For example, the metal wire 158 maybe made from the same material as the base material layer 114 of thesheet metal pieces 112. Or the additional material may be an alloy ofconstituents, some or all of which are also present in the base materiallayer of the sheet metal pieces. Where the sheet metal pieces are coatedsteel sheets, the additional material 152 may be steel or anotherFe-alloy. In another embodiment, the additional material is selected sothat the final weld joint composition has a higher resistance tocorrosion or oxidation than does the base material layer of the sheetmetal pieces. It is not necessary for the additional material to beprovided in wire form, as the additional material could just as easilybe provided in the form of a metallic powder (FIG. 6) that is sprayed oris otherwise provided to the molten weld pool, for example.

In addition to diluting unwanted constituents, the introduction ofadditional material can affect the weld joint composition in other ways.For example, the additional material can be selected to enhance thestrength or hardness of the weld joint 148. In one embodiment, the basematerial layers 116 are steel alloys, and carbon powder is added to theweld pool 146. Carbon can increase the hardness of the weld joint 148 inthis case, even when added in very small amounts (e.g., 0.25 wt % orless). Other materials that may be added to the weld pool 146 to enhancethe strength of the formed weld joint 148 include steel, iron, boron,chromium, magnesium, manganese, molybdenum, tin, titanium, vanadium orany alloy and/or combination thereof. Other added materials may besuitable, including flux-core and solid-core wires, depending on thecomposition of the base material layer, the desired propertyenhancement, or on other factors. Preferably, such materials are addedin an amount that causes the weld joint to have a hardness and/or atensile strength that is greater than that of the sheet metal pieces atlocations away from the weld joint, even after subsequent heat treatingprocesses.

For example, when the welded blank assembly undergoes subsequent heattreating processes without the added material, the composition and themicrostructure of the weld joint and of the base material layer canbecome nearly identical, so that the weld joint is the weakest portionof the welded blank assembly due to surface irregularities and reducedthickness. In the specific case of steel alloys, the weld joint asinitially formed may be harder and stronger than the base material layeraway from the weld joint; but subsequent heat treatments, such ashot-stamping and hot-forming operations, can austenize the weld joint orotherwise make the steel microstructure throughout the welded blankassembly more uniform. In a non-limiting example of a heat treatmentcycle for boron steel, the welded blank assembly may first be heated toan Austenizing temperature, typically around 790 C to 915 C, and thenquickly quenched to form a Martensite grain structure throughout thewhole part; tailored heating and cooling can also be used to effect theformation of the Martensite grains. This is, of course, only one exampleof a heat treatment that may be used with the present welded blankassembly, as others are certainly possible. The terms “heat treatment”and “heat treating,” as used herein, broadly include any type of hightemperature process (e.g., hot stamping) that is known in the art to beuseful with high-strength or hardenable steel alloys, such as boronsteel and HSLA steel.

It is also possible to use the additional material to control the sizeof the resulting weld joint 148, as this may be particularly usefulconsidering that material removed from the weld notches may need to bereplaced in order to achieve a desired strength across the weld joint.The weld notches may be further filled-in with the additional materialduring the process, as shown in FIGS. 5 and 6 where more of the weldnotch volume is filled in than in FIG. 4 where no additional material isadded. In one embodiment, the volumetric amount of additional materialper unit length that is added back to the weld joint 148 is equal to orgreater than the volumetric amount of material per unit length that wasremoved from the edge region 120 prior to welding during the formationof one or both of the weld notches 130. The additional material mayresult in added thickness at the weld joint—e.g., the thickness of theweld joint can be greater than or equal to at least one of thethicknesses _(T1), _(T2) of the adjacent sheet metal pieces so that aportion of the weld joint extends beyond at least one of the adjacentsurfaces of the sheet metal pieces. This may occur, for example, atupper side 124, lower side 126, or both, as illustrated in FIGS. 8-10.

The additional material may also be used to control the shape orgeometry of the resulting weld joint 148, as mentioned above. Forinstance, tailor welded blanks can sometimes exhibit weld joints thatare concave in shape on the upper side where they are laser welded(i.e., side 124, 124′ in the drawings). This is usually because gravitypulls the molten weld material downwards during the laser weldingprocess so that the resulting weld joint 148 is slightly concave orindented on the upper surface. The introduction of additional material,particularly when provided from wire 158, can be used to influence orcontrol this shape so that both sides of the weld joint 148 exhibit anoutwardly extending or convex weld joint shape, as shown in FIGS. 8-10.Controlling the shape of the weld joint 148 and building it up in thethickness direction is different than simply adding filler material tofill in gaps or spaces between the edge surfaces 128, 128′, as issometimes done during certain non-laser welding operations. It should beappreciated that additional material, whether it be provided in wire,powder or some other suitable form, may be used to manipulate the weldjoint 148 and provide it with a shape, other than the convex shapeillustrated in the drawings.

The embodiment of FIG. 5, where additional material is provided to theweld pool 146 in the form of a wire or rod 158, is particularly wellsuited for influencing the composition, size and/or shape of theresultant weld joint 148. If the wire 158 is used to influence the sizeand/or shape of the weld joint 148, it is usually helpful to introducethe wire of additional material on the side of the welded assembly wherethe laser 142 impinges or strikes the work piece. In FIG. 5, this alsohappens to be the upper side of the welded assembly so that as moltenmaterial in the weld pool 146 is pulled down by gravity, it isreplenished and then some by the introduction of the additional materialfrom wire 158. The FIG. 6 embodiment, which depicts an example ofproviding additional material to the weld pool 146 in the form of powderas opposed to wire, is well suited for controlling the composition ofthe resultant weld joint 148. As explained above, it sometimes takesonly a small amount of a strengthening agent like carbon (C) to make theweld joint 148 considerably stronger; thus, the powder introductiontechnique may be best for instances where it is desired to influence thecomposition, but not necessarily the size and/or shape of the weldjoint. That is not to say, however, that the powder introduction methodof FIG. 6 could not be used to control the size and/or shape of the weldjoint, only that it is well suited for controlling its composition ormakeup.

In those examples where a fiber laser or other high energy density laseris used to form the weld joint 148, the additional material may beintroduced to the weld pool 146 by inserting it or otherwise providingit down into a keyhole weld. This can create better uniformity of theweld joint composition, as the additional material does not necessarilyconcentrate at the surface where it is introduced. For uneven gaugewelded blank assemblies (like those shown in FIGS. 7 and 8), controllingthe size and/or shape of the weld joint 148 with additional material maynot be as significant, because material from the thicker sheet metalpiece 112 may be used at the weld pool 146 to address a concavity orthinning of the weld joint 148. For even gauge welded blank assemblies(like those shown in FIGS. 9 and 10), controlling the size and/or shapeof the weld joint 148 with additional material may be more significant,because there is no excess material from a thicker sheet metal piece atthe weld pool 146 that can be used to manipulate the size and/or shapeof the weld joint 148. In these instances, it may be preferable toprovide the additional material from a wire or rod, as they aresometimes better suited to controlling the shape and/or size of the weldjoint 148, as explained above.

FIGS. 7 and 8 are cross-sectional views of the welded blank assembly 140from FIG. 4, respectively taken before or ahead of the laser beam 142and after or behind the laser beam as it moves in the x-direction.Certain dimensional relationships may be described with reference tothese figures. FIG. 7 shows the edge regions 120 of the two sheet metalpieces 112, 112′ with respective edges 128 butted against one another,where one sheet metal piece 112 has a thickness T₁ and the other sheetmetal piece 112′ has a smaller thickness T₂. FIG. 7 also shows the laserbeam 142, complete with a central axis A that forms an angle α with aline B that is normal to the plane of the sheet metal pieces 112. Thefirst sheet metal piece 112 includes weld notches 130 on opposite sides124, 126 of the edge region 120 with respective widths W₁ and W₂. Thesecond sheet metal piece 112′ includes weld notches 130′ on oppositesides 124′, 126′ of the edge region 120′ with respective widths W₃ andW₄. Each weld notch 130, 130′ has a corresponding depth D₁-D₄, as well.

FIG. 8 shows the two sheet metal pieces 112, 112′ joined at the weldjoint 148 to form the welded blank assembly 140. The sheet thicknesses(T₁, T₂), the weld notch widths (W₁-W₄), and the weld notch depths(D₁-D₄) are omitted in FIG. 8 for clarity, but may be the same as inFIG. 7. The welded blank assembly 140 has a weld region 150 thatincludes the weld joint 148, a heat-affected zone 152, and one or moreweld notch surfaces 132, 132′, 134, 134′ (optional) along one or bothsides of the weld joint 148. The weld joint 148 includes material fromboth of the sheet metal pieces 112, 112′, as well as any additionalmaterial that may have been added, and has a width W₅. The weld joint148 may be formed from material that was molten and part of the weldpool 146 during the welding process. A mixture of material from the basematerial layers 114, 114′ of each sheet metal piece 112, 112′ ispreferably the major constituent of the weld joint 148. The weld joint148 is substantially free from material from the coating material layers118, 118′; “substantially free,” as used herein, means that materialfrom the coating material layers 118, 118′ makes up less than 0.5 wt %of the weld joint composition, and in some cases less than 0.1 wt %.Depending on the size and shape of the weld notches 130, 130′, as wellas other factors like the thickness of the various material layers, theweld joint 148 may or may not be substantially free from material fromthe intermediate material layers 116, 116′. In the event that the weldjoint 148 is substantially free of such material, the total amount ofmaterial from the intermediate material layers 116, 116′ is less than0.5 wt % of the weld joint composition. This is not necessary, however,as the weld joint 148 may be substantially free of coating layermaterial, but include intermediate layer material.

The heat-affected zone 152 may be created during the laser weldingprocess and is located adjacent to the weld joint 148. The boundaries ofthe exemplary heat-affected zone 152 are illustrated in dashed lines,however, these boundaries may differ in other embodiments. Thecomposition of the heat-affected zone 152 is generally the same as thebase material layer 114, 114′ from which it is derived. But theheat-affected zone 152 is characterized by having at least a somewhatdifferent microstructure than that of the base material layer 114, dueto the material having reached a transformation temperature during thewelding process. The microstructure in the heat-affected zone 152 can bedifferent from that of the base material layer 114 in several ways, suchas average grain size, grain composition, relative amounts of certainsolid solution phases and/or precipitate phases, crystalline structure(e.g., ferrite versus austenite), etc. In other words, the thermalenergy from the laser beam 142 causes the material in the heat-affectedzone 152 to be heat-treated during the welding process. Together, theweld joint 48 and the heat-affected zone 152 have a width W₆.

In the example shown in FIGS. 7 and 8, the thickness T₁ of sheet metalpiece 112 is greater than the thickness T₂ of sheet metal piece 112′(i.e., an uneven gauge tailor welded blank), although this is notmandatory. A welded blank assembly 140 with thick and thin portions isuseful for subsequent forming of components in which higher strength isrequired at one portion than at another. Thus, thicker metal may be usedonly where needed. Side 126 of the first sheet metal piece 112 isaligned generally in the same plane with side 126′ of the other piece112′ in the welding set-up. The mismatch in sheet thickness causes astep portion so that the edge 128 of the thicker sheet metal piece 112is exposed where it butts against opposing edge 128′. In the illustratedexample, the angle of incidence of laser beam 142 is greater than zero(α>0° so that the laser beam impinges a portion of edge 128 along withweld notch surfaces 134, 134′ during the welding process. The angle ofincidence α and the exact location of the laser spot 144 may varydepending on several factors, such as the actual thicknesses T₁ and T₂and/or the degree of difference between them. For example angle α may belarger with an increased thickness differential (T₁−T₂) or smaller withdecreased thickness difference. In one example angle α=0° when T₁=T₂,and angle α is between 0° and 45°, or even between 5° and 35°, whenT₁≠T₂.

Each weld notch 130, 130′ may be sized individually to ensure thatmaterial from the coating material layers 118, 118′ is not present or issubstantially free from the resulting weld joint 148. For the sheetmetal piece 112, the weld notch dimensions may be correlated to: theoverall thickness T₁ of the sheet metal piece 112, the relativethicknesses of the two sheet metal pieces (e.g., T₁−T₂ or T₁/T₂), thethickness of one or more of the material layers 116, 118, the intendedsize W₅ of the weld joint 148, the intended size W₆ of the heat-affectedzone 152, the size of the laser spot 144, and/or the angle of incidenceα, to cite several non-limiting possibilities.

In the example where the weld notch dimensions are correlated to theoverall thicknesses of the sheet metal pieces, each weld notch 130, 130′may have a width W₁, W₂, W₃, W₄ that is in a range from about 1.0 toabout 2.0 times the thickness T₁, T₂ of the sheet metal piece in whichit is formed. To illustrate this feature, consider the example where T₁is 2.0 mm and T₂ is 1.0 mm, which results in weld notch dimensions W₁and W₂ that are in a range from about 2.0 to 4.0 mm, and W₃ and W₄ thatare in a range from about 1.0 to 2.0 mm. It may be preferable for eachweld notch width W to be near the middle of these ranges so that W₁ andW₂ are each about 1.5T₁, and W₃ and W₄ are each about 1.5T₂. The weldnotch width on one side of a sheet metal piece may be different thanthat on the opposite side of the sheet metal piece. For instance, theweld notch widths W₁ and W₃ on the side of the sheet metal piece that isimpinged or struck by laser beam 142 may be wider than the weld notchwidths W₂ and W₄ on the opposite or non-laser side in order toaccommodate the larger weld joint dimensions. In one embodiment, theratios W₁/W₂ and W₃/W₄ are each in a range from about 1.0 to about 2.0.

In the example where the weld notch dimensions are correlated to theintended sizes of the weld joint and/or the heat-affected zone, thecombined weld notch width (W₁+W₃) on the laser welded side 124 of thewelded blank assembly 140 is from about 2.0 to about 5.0 times theintended size W₅ of the weld joint 148 or from about 1.5 to about 4.0times the intended size W₆ of the heat-affected zone 152. This can allowfor sufficient space in the weld region 50 to help prevent melting andinclusion of material from the coating material layers 118, 118′ duringthe welding process. If the weld notches 130, 130′ are not properlysized, then the laser beam 142 could cause material from one or morecoating or intermediate layers to undesirably flow into the weld pool,thus defeating the purpose of the weld notches. Particularly ininstances where the coating material layer 118 has a lower melting pointthan the base material layer 114, it may be useful to provide weld notchdimensions that are large enough so that the remaining coating materialis spaced sufficiently away from the weld joint 148 and theheat-affected zone 152. On the other hand, if the weld notch dimensionsare too large, then an excessive amount of non-coated surface area maybe exposed at the weld notch surface 134, 134′ which can lead toundesirable corrosion, oxidation, etc. during subsequent heattreatments.

In the example where the weld notch dimensions are correlated to thesize of the laser spot, the narrowest weld notch width W₁, W₂, W₃, W₄may range from about 0.5 to about 2.0 times the width of the laser spot144. Depending on the type of laser and the particular application inwhich it is being used, the laser spot 144 may have a width or diameterfrom about 0.5 mm to about 2.0 mm. Using an example where the width ofthe laser spot 144 is 1.0 mm and the narrowest or smallest weld notchwidth belongs to the weld notch 130′ located on the underside 126′ ofthe welded blank assembly, that weld notch may have a width of W₄ thatis from about 0.5 mm to about 2.0 mm. This relationship can be used inreverse as well to determine suitable laser spot sizes having known weldnotch widths, and vice-versa.

Experience has shown that the preceding relationships involving weldnotch dimensions and one or more parameters—like the overall thicknessof the sheet metal pieces or the intended size of the weld joint and/orheat-affected zone or the size of the laser spot—help ensure that theresulting weld joint will be substantially free of contaminants, andhelp avoid large and superfluous weld notch surface areas surroundingthe weld joint. Such surface areas are not part of the weld joint andhave had coating material layer 118 removed, thus, they can be moresusceptible to corrosion, oxidation, etc.

FIGS. 9 and 10 illustrate additional embodiments of welded blankassemblies that may be formed by a welding process similar to that shownin FIG. 4. The welded blank assembly 240 of FIG. 9 includes sheet metalpieces 212, 212′ that each has generally the same thickness, so thatT₁=T₂ (i.e., an even gauge tailor welded blank). This configuration maybe useful, for example, where it is desired to join two sheet metalpieces having different properties (e.g., different grades of steel sothat one portion of the blank assembly is more formable and anotherportion is harder) or to join two sheet metal pieces made from the samestock material, but in a manner that saves material and reduces waste.In the illustrated embodiment, both of the sheet metal pieces 212, 212′are coated metal pieces and have weld notch surfaces 232, 234 in theweld zone 250. The dimensional relationships set forth above in relationto FIGS. 7 and 8 may apply here as well. Although T₁=T₂ in this example,W₁ is not necessarily equal to W₃, nor is W₂ necessarily equal to W₄,etc.

FIG. 10 illustrates an embodiment in which the welded blank assembly 340includes a coated sheet metal piece 312 and an uncoated sheet metalpiece 312′, with or without the presence of additional material. Thecoated piece 312 has weld notches 330 formed along the edge region priorto welding so that the welded blank assembly 340 includes weld notchsurfaces 332, 334 on one side of the weld zone 350, but not on the otherside of the weld zone where the uncoated piece 312′ is located. Thisconfiguration may be useful in situations where only one coated sheetmetal piece is necessary or desired. The dimensional relationships setforth above in relation to FIGS. 7 and 8 apply here as well. Although T₁is approximately equal to T₂ in this example, this is not always thecase. For example, the coated sheet metal piece 312 may include a higherstrength alloy as the base material layer 14 so that its thickness canbe reduced compared to the uncoated sheet metal piece 312′.

Other types of welding processes may be used in place of the laserwelding processes illustrated and described herein. For example, thelaser beam may be replaced with conventional MIG or TIG, laser MIG orTIG, hybrid welding, or other arc welding equipment to form the weldjoint. Though the inclusion of weld notches along edge regions of sheetmetal pieces may be particularly suitable for use in laser weldingprocesses, where the primary source of weld joint material is the sheetmetal pieces themselves, weld notches can be used with other types ofwelding processes as well and may improve weld joint qualityaccordingly. In addition to the butt weld configurations shown in thefigures, it is also possible to form lap welds or spot welds in whichthe edge regions of two different sheet metal pieces overlap. Inapplications where coated sheet metal pieces are used, the weld notchesdescribed herein may be formed along the edge(s) to be welded to ensurea high quality weld joint.

It is to be understood that the foregoing description is not adefinition of the invention, but is a description of one or morepreferred exemplary embodiments of the invention. The invention is notlimited to the particular embodiment(s) disclosed herein, but rather isdefined solely by the claims below. Furthermore, the statementscontained in the foregoing description relate to particular embodimentsand are not to be construed as limitations on the scope of the inventionor on the definition of terms used in the claims, except where a term orphrase is expressly defined above. Various other embodiments and variouschanges and modifications to the disclosed embodiment(s) will becomeapparent to those skilled in the art. All such other embodiments,changes, and modifications are intended to come within the scope of theappended claims.

As used in this specification and claims, the terms “for example,”“e.g.,” “for instance,” “such as,” and “like,” and the verbs“comprising,” “having,” “including,” and their other verb forms, whenused in conjunction with a listing of one or more components or otheritems, are each to be construed as open-ended, meaning that that thelisting is not to be considered as excluding other, additionalcomponents or items. Other terms are to be construed using theirbroadest reasonable meaning unless they are used in a context thatrequires a different interpretation.

1. A method of making a welded blank assembly, comprising the steps of:(a) providing first and second sheet metal pieces, at least one of thefirst and second sheet metal pieces comprises: a base material layer ofboron steel or press hardenable steel having a thickness in a range from0.5 mm to 2.0 mm, an aluminum-based coating material layer having athickness in a range from 5 μm to 100 μm, and a weld notch located alongan edge region of the sheet metal piece where at least a portion of thecoating material layer has been removed; (b) arranging the first andsecond sheet metal pieces together at the edge region; (c) forming aweld pool between the first and second sheet metal pieces at the edgeregion, wherein the weld pool comprises constituents of the edge region;and (d) providing additional material to the weld pool to influence acomposition of a weld joint that is formed when the weld poolsolidifies, the additional material being provided with a compositionand in an amount that, when the welded blank assembly is subsequentlyheated and quenched in a heat treating process, provides the heattreated weld joint with a hardness and/or a tensile strength that isgreater than that of at least one of the first and second sheet metalpieces at a location away from the heat treated weld joint.
 2. Themethod of claim 1, wherein the base material layer of at least one ofthe first and second sheet metal pieces is boron steel having acomposition that includes base steel alloy and small amounts of atomicboron, whereby an increase in hardness of the boron steel is greaterthan an increase in hardness of the base steel alloy when subjected tothe heat treating process.
 3. The method of claim 1, wherein the basematerial layer of at least one of the first and second sheet metalpieces is press hardenable steel having a composition that allows fordirect or indirect press hardening in conjunction with the heat treatingprocess, whereby an increase in hardness of the press hardenable steelis greater than an increase in conventional steel when subjected to theheat treating process.
 4. The method of claim 1, wherein the at leastone sheet metal piece further comprises an iron-aluminum intermetalliccompound between the base material layer and the coating material layer,both the coating material layer and the intermetallic compound have beenremoved at the weld notch so that the base material layer is exposedalong the edge region as provided in step (a), and the weld pool issubstantially free of both the coating material layer and theintermetallic compound.
 5. The method of claim 1, wherein the at leastone sheet metal piece further comprises an iron-aluminum intermetalliccompound between the base material layer and the coating material layer,the intermetallic compound is present at the weld notch, in the weldpool, and in the resulting weld joint.
 6. The method of claim 1, whereinthe weld pool includes aluminum and the additional material is providedin an amount that dilutes the weld pool and reduces the relative amountof aluminum in the resulting weld joint.
 7. The method of claim 1,wherein both first and second sheet metal pieces have a boron steel basematerial layer, the base material layer of each of the first and secondsheet metal pieces is made from a different grade of steel so that afirst portion of the welded blank assembly is more formable than asecond portion and so that the second portion of the welded blankassembly is harder than the first portion.
 8. The method of claim 1,wherein step (d) further comprises introducing the additional materialto the weld pool at a keyhole weld formed by a high energy density laserto thereby enhance the uniformity of the composition of the formed weldjoint.
 9. The method of claim 1, further comprising the step of: heattreating the welded blank assembly as part of a hot stamping processthat includes heating the welded blank assembly to an austenizingtemperature and subsequently quenching the welded blank assembly to forma martensite grain structure throughout the welded blank assembly. 10.The method of claim 1, wherein the additional material is provided tothe weld pool in the form of a wire.
 11. The method of claim 1, whereinthe additional material includes iron, carbon, steel, boron, chromium,magnesium, manganese, molybdenum, tin, titanium, vanadium or any alloyor combination thereof.
 12. A method of making a welded blank assembly,comprising the steps of: (a) providing first and second sheet metalpieces, at least one of the first and second sheet metal piecescomprises: a base material layer of boron steel or press hardenablesteel having a thickness in a range from 0.5 mm to 2.0 mm, analuminum-based coating material layer having a thickness in a range from5 μm to 100 μm, and a weld notch located along an edge region of thesheet metal piece where at least a portion of the coating material layerhas been removed; (b) arranging the first and second sheet metal piecestogether at the edge region; (c) forming a weld pool between the firstand second sheet metal pieces at the edge region, wherein the weld poolcomprises constituents of the edge region; (d) solidifying the weld poolto form a weld joint that joins the first and second sheet metal piecestogether at a weld region of the welded blank assembly; and (e) using asecondary heat source to heat a protective material comprising aluminumso that the protective material flows in the weld region after the weldpool is at least partially solidified.
 13. The method of claim 12,wherein at least a portion of the protective material is material fromthe coating material layer that has been displaced from the weld notchbut remains alongside the weld notch as part of the sheet metal piece,the displaced material being heated and at least partially liquefied bythe secondary heat source to flow in the weld region after the weld poolis at least partially solidified to cover and protect at least a portionof the weld region.
 14. The method of claim 12, wherein at least aportion of the protective material is from an additionally providedmaterial that is not part of the sheet metal pieces provided in step(a), the additionally provided material being heated and at leastpartially liquefied by the secondary heat source to flow in the weldregion after the weld pool is at least partially solidified to cover andprotect at least a portion of the weld region.
 15. The method of claim12, wherein the base material layer of at least one of the first andsecond sheet metal pieces is boron steel having a composition thatincludes a base steel alloy and small amounts of atomic boron, wherebyan increase in hardness of the boron steel is greater than an increasein hardness of the base steel alloy when subjected to the heat treatingprocess.
 16. The method of claim 12, wherein the base material layer ofat least one of the first and second sheet metal pieces is presshardenable steel having a composition that allows for direct or indirectpress hardening in conjunction with the heat treating process, wherebyan increase in hardness of the press hardenable steel is greater than anincrease in conventional steel when subjected to the heat treatingprocess.
 17. The method of claim 12, wherein the at least one sheetmetal piece further comprises an iron-aluminum intermetallic compoundbetween the base material layer and the coating material layer, both thecoating material layer and the intermetallic compound have been removedat the weld notch so that the base material layer is exposed along theedge region as provided in step (a), and the weld pool is substantiallyfree of both the coating material layer and the intermetallic compound.18. The method of claim 12, wherein the at least one sheet metal piecefurther comprises an iron-aluminum intermetallic compound between thebase material layer and the coating material layer, the intermetalliccompound is present at the weld notch, in the weld pool, and in theresulting weld joint.
 19. The method of claim 12, wherein both first andsecond sheet metal pieces have a boron steel base material layer, thebase material layer of each of the first and second sheet metal piecesis made from a different grade of steel so that a first portion of thewelded blank assembly is more formable than a second portion and so thatthe second portion of the welded blank assembly is harder than the firstportion.
 20. The method of claim 12, further comprising the step of:heat treating the welded blank assembly as part of a hot stampingprocess that includes heating the welded blank assembly to anaustenizing temperature and subsequently quenching the welded blankassembly to form a martensite grain structure throughout the weldedblank assembly.
 21. The method of claim 12, further comprising the stepof providing additional material to the weld pool to influence acomposition of the formed weld joint, the additional material beingprovided with a composition and in an amount that, when the welded blankassembly is subsequently heated and quenched in a heat treating process,provides the heat treated weld joint with a hardness and/or a tensilestrength that is greater than that of at least one of the first andsecond sheet metal pieces at a location away from the heat treated weldjoint.
 22. A method of making a welded blank assembly, comprising thesteps of: (a) providing first and second sheet metal pieces, at leastone of the first and second sheet metal pieces comprises: a basematerial layer of boron steel or press hardenable steel having athickness in a range from 0.5 mm to 2.0 mm, an aluminum-based coatingmaterial layer having a thickness in a range from 5 μm to 100 μm, and aweld notch located along an edge region of the sheet metal piece whereat least a portion of the coating material layer has been removed; (b)arranging the first and second sheet metal pieces together at the edgeregion; (c) forming a weld pool between the first and second sheet metalpieces at the edge region, wherein the weld pool comprises constituentsof the edge region; and (d) solidifying the weld pool to form a weldjoint that joins the first and second sheet metal pieces together at aweld region of the welded blank assembly with a heat affected zoneadjacent the formed weld joint, wherein each weld notch is provided witha width so that a combined weld notch width is in a range from 1.5 to4.0 times a width of the heat-affected zone.
 23. The method of claim 22,wherein the combined weld notch width is also in a range from 2.0 to 5.0times a width of the formed weld joint.
 24. The method of claim 22,wherein the width of each weld notch is in a range from 0.5 to 2.0 timesa thickness of the sheet metal piece in which it is provided.
 25. Themethod of claim 22, wherein the base material layer of at least one ofthe first and second sheet metal pieces is boron steel having acomposition that includes a base steel alloy and small amounts of atomicboron, whereby an increase in hardness of the boron steel is greaterthan an increase in hardness of the base steel alloy when subjected tothe heat treating process.
 26. The method of claim 22, wherein the basematerial layer of at least one of the first and second sheet metalpieces is press hardenable steel having a composition that allows fordirect or indirect press hardening in conjunction with the heat treatingprocess, whereby an increase in hardness of the press hardenable steelis greater than an increase in conventional steel when subjected to theheat treating process.
 27. The method of claim 22, wherein the at leastone sheet metal piece further comprises an iron-aluminum intermetalliccompound between the base material layer and the coating material layer,both the coating material layer and the intermetallic compound have beenremoved at the weld notch so that the base material layer is exposedalong the edge region as provided in step (a), and the weld pool issubstantially free of both the coating material layer and theintermetallic compound.
 28. The method of claim 22, wherein the at leastone sheet metal piece further comprises an iron-aluminum intermetalliccompound between the base material layer and the coating material layer,the intermetallic compound is present at the weld notch, in the weldpool, and in the resulting weld joint.
 29. The method of claim 22,wherein both first and second sheet metal pieces have a boron steel basematerial layer, the base material layer of each of the first and secondsheet metal pieces is made from a different grade of steel so that afirst portion of the welded blank assembly is more formable than asecond portion and so that the second portion of the welded blankassembly is harder than the first portion.
 30. The method of claim 22,further comprising the step of: heat treating the welded blank assemblyas part of a hot stamping process that includes heating the welded blankassembly to an austenizing temperature and subsequently quenching thewelded blank assembly to form a martensite grain structure throughoutthe welded blank assembly.
 31. The method of claim 22, furthercomprising the step of providing additional material to the weld pool toinfluence a composition of the formed weld joint, the additionalmaterial being provided with a composition and in an amount that, whenthe welded blank assembly is subsequently heated and quenched in a heattreating process, provides the heat treated weld joint with a hardnessand/or a tensile strength that is greater than that of at least one ofthe first and second sheet metal pieces at a location away from the heattreated weld joint.
 32. The method of claim 22, further comprising thestep of using a secondary heat source to heat a protective materialcomprising aluminum so that the protective material flows in the weldregion after the weld pool is at least partially solidified.